1. Field of the Invention
The present invention relates to an image processing method in which, upon discrimination of the image, the image signals are converted into binary signals by a means corresponding to the kind of the image.
2. Description of the Prior Art
In recent years, a remarkable increase in the capacity has been attained in the mediums such as RAMs, hard discs, optical discs and magnetic discs, due to the development of memories of large storage capacities, thanks to a progress in the electronic technologies. In addition, there is a rapid movement for putting optical discs into practical use, as well as development and studies on the magnetic discs and, nowadays, it is possible to write image information in such recording mediums. For instance, an optical disc can store about 10,000 (ten thousand) sheets of A-4 size documents. It is, therefore, a current tendency to use the memories of large capacities, for the storage of the image information. Attempts have been also made to code and compress the image information to be written, in order to further increase the amount of storage of the image information in the memory.
On the other hand, there is an increasing demand for making a hard copy of the image information read out of the memory. Various recording systems are available for this purpose. In the case of heat-sensitive recording system, the recording speed is too low, although it permits an output on the order of 16 grades of gradation. On the other hand, electrostatic recording system (multi stylus system) suffers from a problem that the gradation reproduction is affected too much by the environmental condition, although the recording speed can be increased. Under these circumstances, an image recording system making use of binary dots (white and black) is attracting attention because it can obviate the above-mentioned problems. In this system, in order to materially reproduce half tone with the apparatus which can record only two values of white and black, it is necessary to convert the image information into binary signals. Some methods have been known as the method for binary coding the picture information, such as the binary coding merely by employing a single threshold value and a method so-called dither method. It is a key for attaining a high quality of the reproduced image to adequately set the threshold value or the dither matrix (threshold value group), in conducting the binary coding.